THE BRACHIOPODA 41 



fossils, and not easily found by collectors when they are 

 preserved. 



In addition to the genera illustrated in Fig. 10, the fol- 

 lowing are noteworthy : 



Ornithella (Figs. 2, 5, b) of the Jurassic, smooth, with 

 straight anterior margin; Aulacotkyris, Jurassic, smooth, 

 with ventral fold and dorsal sinus ; Lyra and Trigonosemus, 

 Cretaceous, plicate forms, with high cardinal areas. 



SUB- ORDER 3. Spiriferacea. Telotremata with cal- 

 careous spirals ; deltidial plates in some cases fused into 

 a single plate. 



Spirifer striatus (Fig. 7, k) of the Carboniferous Lime- 

 stone is a very broad shell, being just about twice as broad 

 as long. The greatest breadth is at the hinge-line, which is 

 straight. Both valves are strongly convex, but the ventral 

 has a deep median sinus, the dorsal a corresponding fold. 

 The surface is ornamented with numerous radiating costae 

 The umbo of the ventral valve is prominent, but not 

 large, and below it is a large cardinal area showing 

 growth-striations at right-angles to the hinge-line ; it 

 includes a triangular delthyrium, in which a large pseudo- 

 deltidium arches over the pedicle-foramen. In the dorsal 

 valve there is a much narrower area. 



The internal structure can only exceptionally be made 

 out. The chief feature is the pair of spirals. Starting 

 from the crura the ribbons first approach one another, 

 and then, as the coiling begins, diverge from one another, 

 so that the apices of the spiral cones are near the outer 

 ends of the hinge-line. From this it would seem that, 

 unlike most other brachiopods, Spirifer had a median 

 inhalent current and a pair of lateral exhalent currents. 

 The first turn of one spiral is joined to that of the other, 

 on the dorsal side, by a simple bar, the jugum. In the 

 ventral valve there are short dental plates. 



Various other species of Spirifer will answer this same 



